Longitudinally coupled resonator type surface acoustic wave filter having narrow electrode finger pitch sections

Abstract

A longitudinally coupled resonator type surface acoustic wave filter includes a piezoelectric substrate and first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs. Each of the first, second and third IDTs has a plurality of electrode fingers. The first and second IDTs have narrow electrode-finger pitch sections that have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other. The second and third IDTs have narrow electrode-finger pitch sections that have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the second and third IDTs adjacent to each other. The electrode-finger pitch of the narrow electrode-finger pitch sections in the first and second IDTs is different from the electrode-finger pitch of the narrow electrode-finger pitch sections in the second and third IDTs.

What is claimed is:  
     
       1. A longitudinally coupled resonator type surface acoustic wave filter comprising: 
       a piezoelectric substrate; and  
       first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers; wherein  
       the first and second IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other;  
       the second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch that is narrower than the remaining electrode-finger pitches, at respective end portions of the second and third IDTs adjacent to each other; and  
       the electrode-finger pitch of the narrow electrode-finger pitch sections in the first and second IDTs is different from the electrode-finger pitch of the narrow electrode-finger pitch sections in the second and third IDTs.  
     
     
       2. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 1 , wherein a number of the electrode fingers of the narrow electrode-finger pitch sections in the first and second IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the second and third IDTs. 
     
     
       3. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 1 , wherein the second IDT has an even number of electrode fingers. 
     
     
       4. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 1 , wherein at least one of the IDTs is subjected to thinning out and weighting. 
     
     
       5. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 4 , wherein the thinning-out and weighting is asymmetrical to the center of the longitudinally coupled resonator type surface acoustic wave filter in the surface wave propagating direction. 
     
     
       6. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 1 , further comprising at least one of a surface acoustic wave resonator connected in series to the longitudinally coupled resonator type surface acoustic wave filter and a surface acoustic wave resonator connected in parallel to the longitudinally coupled resonator type surface acoustic wave filter. 
     
     
       7. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 1 , further comprising a balanced input terminal or an output terminal and an unbalanced output terminal or an input terminal arranged to provide a balance-unbalance conversion function. 
     
     
       8. A communication apparatus comprising the longitudinally coupled resonator type surface acoustic wave filter according to  claim 1 . 
     
     
       9. A longitudinally coupled resonator type surface acoustic wave filter comprising: 
       a piezoelectric substrate; and  
       first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers; wherein  
       the first and second IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other;  
       the second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the second and third IDTs adjacent to each other; and  
       a number of the electrode fingers of the narrow electrode-finger pitch sections in the first and second IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the second and third IDTs.  
     
     
       10. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 9 , wherein the second IDT has an even number of electrode fingers. 
     
     
       11. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 9 , wherein at least one of the IDTs is subjected to thinning out and weighting. 
     
     
       12. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 11 , wherein the thinning-out and weighting is asymmetrical to the center of the longitudinally coupled resonator type surface acoustic wave filter in the surface wave propagating direction. 
     
     
       13. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 9 , further comprising at least one of a surface acoustic wave resonator connected in series to the longitudinally coupled resonator type surface acoustic wave filter and a surface acoustic wave resonator connected in parallel to the longitudinally coupled resonator type surface acoustic wave filter. 
     
     
       14. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 9 , further comprising a balanced input terminal or an output terminal and an unbalanced output terminal or an input terminal arranged to provide a balance-unbalance conversion function. 
     
     
       15. A communication apparatus comprising the longitudinally coupled resonator type surface acoustic wave filter according to  claim 9 . 
     
     
       16. A longitudinally coupled resonator type surface acoustic wave filter comprising: 
       a piezoelectric substrate; and  
       first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers; wherein  
       only the first and second IDTs or only the second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other, or at the respective end portions of the second and third IDTs adjacent to each other.  
     
     
       17. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 16 , wherein the second IDT has an even number of electrode fingers. 
     
     
       18. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 16 , wherein at least one of the IDTs is subjected to thinning out and weighting. 
     
     
       19. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 18 , wherein the thinning-out and weighting is asymmetrical to the center of the longitudinally coupled resonator type surface acoustic wave filter in the surface wave propagating direction. 
     
     
       20. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 16 , further comprising at least one of a surface acoustic wave resonator connected in series to the longitudinally coupled resonator type surface acoustic wave filter and a surface acoustic wave resonator connected in parallel to the longitudinally coupled resonator type surface acoustic wave filter. 
     
     
       21. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 16 , further comprising a balanced input terminal or an output terminal and an unbalanced output terminal or an input terminal arranged to provide a balance-unbalance conversion function. 
     
     
       22. A communication apparatus comprising the longitudinally coupled resonator type surface acoustic wave filter according to  claim 16 . 
     
     
       23. A longitudinally coupled resonator type surface acoustic wave filter comprising: 
       a piezoelectric substrate;  
       a first longitudinally coupled resonator type surface acoustic wave filter unit which includes first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers;  
       a second longitudinally coupled resonator type surface acoustic wave filter unit which includes fourth, fifth and sixth IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the fifth IDT is interposed between the fourth and the sixth IDTs, each of the fourth, fifth and sixth IDTs having a plurality of electrode fingers; wherein  
       the first, second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first, second and third IDTs adjacent to each other;  
       the fourth, fifth and sixth IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the fourth, fifth and sixth IDTs adjacent to each other; and  
       the electrode-finger pitch of the narrow electrode-finger pitch sections in the first, second and third IDTs is different from the electrode-finger pitch of the narrow electrode-finger pitch sections in the fourth, fifth and sixth IDTs.  
     
     
       24. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 23 , wherein a number of the electrode fingers of the narrow electrode-finger pitch sections in the first, second and third IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the fourth, fifth and sixth IDTs. 
     
     
       25. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 23 , wherein the second and fifth IDTs have an even number of electrode fingers. 
     
     
       26. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 23 , wherein at least one of the IDTs is subjected to thinning out and weighting. 
     
     
       27. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 26 , wherein the thinning-out and weighting is asymmetrical to the center of the longitudinally coupled resonator type surface acoustic wave filter in the surface wave propagating direction. 
     
     
       28. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 23 , further comprising at least one of a surface acoustic wave resonator connected in series to the longitudinally coupled resonator type surface acoustic wave filter and a surface acoustic wave resonator connected in parallel to the longitudinally coupled resonator type surface acoustic wave filter. 
     
     
       29. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 23 , further comprising a balanced input terminal or an output terminal and an unbalanced output terminal or an input terminal arranged to provide a balance-unbalance conversion function. 
     
     
       30. A communication apparatus comprising the longitudinally coupled resonator type surface acoustic wave filter according to  claim 23 . 
     
     
       31. A longitudinally coupled resonator type surface acoustic wave filter comprising: 
       a piezoelectric substrate;  
       a first longitudinally coupled resonator type surface acoustic wave filter unit which includes first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs, each of the first, second and third IDTs having a plurality of electrode fingers;  
       a second longitudinally coupled resonator type surface acoustic wave filter unit which includes fourth, fifth and sixth IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the fifth IDT is interposed between the fourth and the sixth IDTs, each of the fourth, fifth and sixth IDTs having a plurality of electrode fingers; wherein  
       the first, second and third IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first, second and third IDTs adjacent to each other;  
       the fourth, fifth and sixth IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the fourth, fifth and sixth IDTs adjacent to each other; and  
       a number of the electrode fingers of the narrow electrode-finger pitch sections in the first, second and third IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the fourth, fifth and sixth IDTs.  
     
     
       32. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 31 , wherein a number of the electrode fingers of the narrow electrode-finger pitch sections in the first, second and third IDTs is different from a number of the electrode fingers of the narrow electrode-finger pitch sections in the fourth, fifth and sixth IDTs. 
     
     
       33. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 31 , wherein the second and fifth ITDs have even electrode fingers. 
     
     
       34. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 31 , wherein at least one of the IDTs is subjected to thinning out and weighting. 
     
     
       35. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 34 , wherein the thinning-out and weighting is asymmetrical to the center of the longitudinally coupled resonator type surface acoustic wave filter in the surface wave propagating direction. 
     
     
       36. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 31 , further comprising at least one of a surface acoustic wave resonator connected in series to the longitudinally coupled resonator type surface acoustic wave filter and a surface acoustic wave resonator connected in parallel to the longitudinally coupled resonator type surface acoustic wave filter. 
     
     
       37. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 31 , further comprising a balanced input terminal or an output terminal and an unbalanced output terminal or an input terminal arranged to provide a balance-unbalance conversion function. 
     
     
       38. A communication apparatus comprising the longitudinally coupled resonator type surface acoustic wave filter according to  claim 31 . 
     
     
       39. A longitudinally coupled resonator type surface acoustic wave filter comprising: 
       a piezoelectric substrate;  
       a first longitudinally coupled resonator type surface acoustic wave filter unit which includes first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTS, each of the first, second and third IDTs having a plurality of electrode fingers;  
       a second longitudinally coupled resonator type surface acoustic wave filter unit which includes fourth, fifth and sixth IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the fifth IDT interposed between the fourth and the sixth IDTs, each of the fourth, fifth and sixth IDTs having a plurality of electrode fingers; wherein  
       only the first, second and third IDTs or only the fourth, fifth and sixth IDTs have narrow electrode-finger pitch sections which have an electrode-finger pitch that is narrower than the remaining electrode-finger pitches, at respective end portions of the first, second and third IDTs adjacent to each other, or at respective end portions of the fourth, fifth and sixth IDTs adjacent to each other.  
     
     
       40. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 39 , wherein the second and fifth IDTs have an even number of electrode fingers. 
     
     
       41. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 39 , wherein at least one of the IDTs is subjected to thinning out and weighting. 
     
     
       42. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 41 , wherein the thinning-out and weighting is asymmetrical to the center of the longitudinally coupled resonator type surface acoustic wave filter in the surface wave propagating direction. 
     
     
       43. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 39 , further comprising at least one of a surface acoustic wave resonator connected in series to the longitudinally coupled resonator type surface acoustic wave filter and a surface acoustic wave resonator connected in parallel to the longitudinally coupled resonator type surface acoustic wave filter. 
     
     
       44. A longitudinally coupled resonator type surface acoustic wave filter according to  claim 39 , further comprising a balanced input terminal or an output terminal and an unbalanced output terminal or an input terminal arranged to provide a balance-unbalance conversion function. 
     
     
       45. A communication apparatus comprising the longitudinally coupled resonator type surface acoustic wave filter according to  claim 39 .